In automobiles, light trailers, and other light-duty applications, it is common for a wheel bearing assembly to be sealed relatively permanently for all or a good part of the service life of the assembly. Thus, automotive applications, permanently greased bearing assemblies are covered by opaque hubcaps (as opposed to decorative wheel covers which are sometimes incorrectly called hubcaps) which are never removed except for repairs, or for replacement of bearings and/or seals. In most cases, the bearings are permanently lubricated, or are lubricated by a supply of grease coming from another portion of the sealed assembly as a whole.
In the case of large, over-the-road truck tractors and semi-trailers, and other heavy-duty applications, however, the situation is different. Vehicles of these types have extended service lives both in terms of years and in terms of miles traveled. Wheel bearing assemblies are critical components of vehicles such as these. Most commonly, these wheel assemblies include a large, heavy-duty spindle and bearings supportingly engaging one or more rotatable parts, including a rotatable hub portion that in turns supports a brake drum and a removable wheel. In driven wheel applications, the bearings usually rest in the axle housing so that the driving axle is not subject to bending loads. In these cases, while the axle housing takes most or all of the load transmitted from the tires and wheels, and these bearing sets also include one or more oil or grease seals to retain the lubricant within the sealed region, and therefore also require hubcaps.
A number of years ago, many manufacturers and fleet operators, with the aid of bearing and seal suppliers, discovered that the life of ball or roller bearing type assemblies could be extended substantially by using oil rather than grease as the lubricant. Thus, the oil, although more fluent (less viscous) than grease, successfully addressed the problems of flushing dirt from the interfaces between metal parts. Modern oils are also formulated in such a way as to suspend entrained dirt and various other residues within the oil. In this way, as in automotive crankcases or other applications, the oil can be periodically drained and replaced with new, fresh oil, thus removing the grit and contaminants. This concept was brought to practical reality by the development of seals capable of handling low viscosity oils opposed to merely being able to impede leakage of semi-solid or gel materials such as greases.
With the popularization of this concept, hubcaps have been called upon to serve functions in addition to that of merely being a static seal. By "static seal" or "secondary seal," as used herein is meant a seal wherein there is no relative movement of the two or more sealed parts; "primary" or similar expression is applied to a seal application wherein there is relative movements between the sealed parts.
First, the hubcap must be oil-impermeable and provide a positive mechanical barrier against the entrance of contaminants. In addition, the hubcap should be able to provide a transparent window to permit external examination of the sealed region, including the oil level. Moreover, the hubcap should optionally afford means of not only observing, but also replenishing oil so as to maintain a proper oil level in the sealed region.
Preferably, the access plug arrangement should be such that it may provide or be compatible with venting systems and also be constructed and arranged so as to resist accidental or negligent damage removal or disassembly.
Another desirable characteristic in a heavy-duty vehicle hubcap is that of structural strength and integrity, whereby minor collisions with road debris, stones, and the like, or occasional contact with a stationary objects such as posts or curbs in a loading/unloading zone or dock will not damage the hubcap.
Still another desirable characteristic of such a hubcap is that one product be adaptable to several applications. This concept is sometimes referred to as "universality" or "interchangeability." A universal or highly interchangeable part thus simplifies problems of inventory control and stocking, requiring fewer "part numbers" to service a variety of applications than would be the case where each individual application required a different part. Thus, universality lowers not only inventory costs, but also reduces tooling costs and other costs associated with manufacturing the product.
In addition to structural integrity and universality, it is also desirable that the static seal mechanism between the hubcap and the other components be independent of the fasteners in the sense that the fasteners should not be called upon to seal the lubricant or exclude liquid or solid contaminants.
It is also desirable from a design and engineering standpoint that individual components of the hubcap be able to withstand the loads expected to be imposed upon them without being unnecessarily massive in non-load bearing areas.
Another preferred characteristic is that the hubcap be able to be manufactured readily at low cost, and to the extent that different elements of the hubcap are required to be different for different applications, that such elements can be interchanged during the manufacturing process. Thus, for example, if a part that is to accommodate a different bolt shank size or bolt pattern is to be provided, it should be easily interchangeable, as should be the window or the like if it is to provide an access opening of a different size, contour, or inside diameter. The ability to provide a mold and method that will accommodate these changes without requiring any tooling changes, or at least extensive tooling changes, is also advantageous, and, consequently, there is a need for economical, effective methods of making such a hubcap. A satisfactory process would also be able to provide a permanent, liquid-tight bond between mating parts that may be formed separately and incorporated into the product as a whole during what is termed an insert molding operation.
In view of the need to provide a hubcap that will combine a number of desirable advantages and characteristics at reasonable cost and will be compatible with economical manufacture, it is an object of the present invention to provide an improved hubcap for heavy duty applications.
Another object of the invention is to provide a hubcap wherein a single unit is able to be used in a number of applications, including those having bolt circle patterns of slightly different diameters.
A further object of the invention is to provide a method and apparatus for manufacturing an improved hubcap.
A still further object is to provide a hubcap combining improved ruggedness and reliability in use, and able to be made by an economical method.
Yet another object of the invention is to provide a hubcap having a window insert received in an face portion of the cap body to permit viewing into the interior of the sealed region.
Another object of the invention is to provide a hubcap wherein opaque and transparent liquid-retaining portions are integrally bonded to one another in a manner not requiring separate gaskets or seals and being leakfree in use.
A further object of the invention is to provide a hubcap which also includes an opening for replenishing or changing oil or other lubricant, with such opening being sealed by a plug that is resistant to unintentional removal.
Still another object of the invention is to provide a hubcap made from different materials but integrally containing a mounting ring insert or like reinforcing insert made of metal or other material having high strength in compression.
A still further object of the invention is to provide a hubcap manufacturing method which includes placing both metal and non-metal inserts in a mold and simultaneously forming the major portions of a hubcap body and bonding them respectively to a window-forming center element and a metal reinforcing ring serving to define the bolt circle about which the fasteners are inserted when securing the hubcap to the hub or end of the axle housing.
One additional object of the invention is to provide a hubcap having a body made from a rugged and durable, non-brittle material, preferably a reinforced plastic material such as a glass-filled nylon or the like, and incorporating other novel features as well.
A still further object of the invention is to provide a hubcap combining a number of advantageous features and characteristics and which can be manufactured reliably and at low cost.
Yet another object of the invention is to provide a hubcap which simplifies inspection and maintenance of sealed wheel assemblies and, which can be made tamperproof without expensive modification.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a hubcap having a body portion that includes a composite mounting flange, a sidewall with an access port and an end wall having a transparent window insert portion received in the end wall in mechanically interlocked and bonded relation, with the composite mounting flange including a mounting ring insert portion providing contoured openings for receiving removable fasteners. The invention also achieves its objects by providing a novel method of making such a hubcap.
The exact manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention described in detail in the following specification and shown in the accompanying drawings, where in like reference numbers indicate corresponding parts throughout.